The present invention relates to an improvement on the wood planer cutterhead design for reduced noise level described in applicant's prior U.S. Pat. No. 4,074,737, the entire disclosure of which is incorporated herein by reference.
In the 1970's, workplace safety and health became a matter of concern. In the woodworking industry, the noise of machinery was excessive and applicant undertook extensive research to isolate and attempt to determine ways to reduce vibration and noise. As a result, the invention of the aforementioned '737 patent came about. Briefly, that patent covers an invention in which the design of a rotating helical cutterhead for a wood planer was devised. The cutterhead typically has more than one knife blade in contact with the workpiece at any instant by satisfying the minimum condition of the formula L=.pi.D cot.phi./N is less than the workpiece width and in which
L is the axial contact distance, PA1 D is the cutterhead diameter, PA1 N is the number of knife blades, PA1 .phi. is the helix angle, and PA1 L is preferably less than 4 inches.
Applying those design criteria to the manufacture of cutterheads successfully led to the reduction of noise in the planing workplace on a substantial basis.
Concerns in addition to noise abatement are also important, and applicant has found that further refinement of the relationship between the helical cutterhead design and the width of the workpiece being planed yield further advantages.
Those advantages are numerous.
The advantages are brought about by assuring that the width dimension of the lumber with respect to the contact distance of the cutterhead not only exceeds the cutterhead contact distance L, but is substantially equal to an integral multiple of the contact distance, whether the integer be 2, 3 or so on.
Making the workpiece width an integer has the effect of further reducing the fluctuating cutting forces and attendant vibration over and above the design described in the '737 patent When the condition that the ratio of the workpiece's width to the cutterhead contact distance is an integer is met, there is minimal net change in fluctuating forces on the workpiece as a helical knife engages the workpiece, because at the same instant another helical knife disengages the workpiece. The reduction in vibration leads to numerous advantages.
First, the chips planed off of the surface of the workpiece are of excellent consistency and quality for chipboard manufacture.
Second, the surface quality in areas around knots is improved.
Third, the reduced cutting forces that occur when the width is an integral multiple of the contact distance lead to longer cutterhead tool life.
Fourth, since reduced vibrational forces are involved, sharper, more brittle tools can be used, increasing the length of the life of the blade required between sharpening.
Fifth, the finish on the surface of the workpiece is of a better and more uniform quality because there is less workpiece vibration.
Sixth, the reduced vibration leads to a longer bearing life for the mounting of the cutterhead on its arbor.
Seventh, with reduced cutting forces, less dense materials such as celotex may be cut.
Eighth, not only is the surface finish of the workpiece of better quality to the eye as unfinished, but after finishing, the quality is even further enhanced. The vibration caused by prior art methods seems to, by some mechanism similar to bruising, cause sub-surface damage. Upon staining of the workpiece, there is uneven stain uptake by the workpiece. By reducing the vibration through the implementation of the present invention, this uneven staining is reduced. Thus, numerous advantages are made possible by the present invention.